1. Field of the Invention
The present invention relates to a multiring control method, a node using the method, and a control program. More particularly, the present invention relates to a method of discarding a ring frame in a multiring and a protection method.
2. Description of the Prior Art
With the increase in traffic of data typified by Internet protocols (IP), a demand for efficient data transmission has arisen even on conventional communication service companies which have mainly offered voice transmission service (hereinafter referred to as “carrier”). Also in the field of data transmission networks, there is a demand for a highly reliable protection method such as one conformable to “SONET, GR-1230-Core, Issue 3 Dec. 1996 Bellcore” on which conventional transmission networks are based. Spatial Reuse Protocol (hereinafter referred to as SRP) (RFC 2892 IETF) can be mentioned as a highly reliable protection method for data transmission networks.
A conventional protection method using SRP will be described with reference to FIGS. 14 to 19. FIG. 15 is a diagram showing a simplified configuration of a ring frame (also referred to as “network node interface (NNI) packet”) 180 used between ring nodes. The ring frame 180 has a transmission destination ring node address 181, a transmission source ring node address 182, a transmission ring ID 183, a time to live (TTL) 184, a frame attribute 185, a flow ID 186, and a user frame 187. A ring node address for a transmission destination is stored as transmission destination ring node address 181. A ring node address for a transmission source is stored as transmission source ring node address 182. An identifier for a ring frame transmission ring, i.e., an inner ring or an outer ring, is stored as transmission ring ID 183. The maximum number of hops that the frame can make in a two-fiber ring is stored as TTL 184. An attribute of the ring frame 180 is stored as frame attribute 185. As ring frame attribute 185, attributes “fault information notice frame” and “data frame” are defined. An ID for identification of a flow is stored as flow ID 186.
FIG. 14 is a diagram showing the configuration of a ring node 100 which is an example of a conventional ring node. Referring to FIG. 14, the ring node 100 is constituted by address comparators 110 and 111, forwarding circuits 120 and 121, multiplexing circuits 130 and 131, a ring protection processing circuit 140, a protection switch 150, a packet switch 160, and a frame conversion circuit 170.
A user frame input through a tributary link 103-in is transferred to the frame conversion circuit 170.
The frame conversion circuit 170 converts the user frame into a ring frame 180. The frame conversion circuit 170 identifies a transmission destination ring node from the transmission destination address in the user frame, stores the address as transmission destination ring node address 181 in the ring frame 180, stores the address of this node as transmission source ring node address 181, and stores various parameters as transmission ring ID 183, TTL 184, frame attribute 185, and flow ID 186. Thereafter, the frame conversion circuit 170 transfers the ring frame 180 to the packet switch 160. The frame conversion circuit 170 also converts a ring frame 180 transferred from the packet switch 160 into a user frame and outputs the user frame through the tributary 103-out.
The packet switch 160 receiving the ring frame 180 from the frame conversion circuit 170 transfers the ring frame 180 to the suitable multiplexing circuit 130 or 131 by referring to the transmission destination ring node address 181 in the ring frame 180. The packet switch 160 also receives a ring frame 180 transferred from the forwarding circuit 120 or 121 and transfers this ring frame 180 to the frame conversion circuit 170.
A ring frame 180 from an inner ring 101-in or an outer ring 102-in is input to the address comparator 110 or 111.
The address comparator 110 or 111 discards the received ring frame 180 in a case where the transmission source ring node address 181 in the ring frame 180 and the address of this node coincide with each other, and where the transmission ring ID 183 and the ID of the ring from which the ring frame 180 has been received coincide with each other. In other cases, the address comparator transfers the ring frame 180 to the forwarding circuit 120 or 121.
The forwarding circuit 120 or 121 transfers the received ring frame 180 to the ring protection processing circuit 140 if the transmission destination ring node address 181 in the ring frame 180 is the same as the address of this node and if the frame attribute 185 is “fault information frame”. The forwarding circuit also transfers the received ring frame 180 to the packet switch 160 if the transmission destination ring node address 181 in the ring frame 180 is the same as the address of this node and if the frame attribute 185 is “user frame”.
Also, the forwarding circuit 120 or 121 makes copies of the ring frame 180 and transfers one of the copies to the packet switch 160 if the transmission destination ring node address 181 coincides with the address of multicasting/broadcasting in which this node participates. The forwarding circuit 120 or 121 subtracts 1 from the TTL value if the transmission destination ring node address 181 in the input ring frame 180 does not coincide with the address of this node, or if the transmission destination ring node address 181 is a multicast/broadcast address. The forwarding circuit 120 or 121 discards ring frame 180 in which the TTL value is zero and transfers other ring frames 180 to the protection switch 150.
The protection switch 150 has a pass mode and a wrap mode. In the pass mode, it transfers a ring frame 180 from the forwarding circuit 120 to the multiplexing circuit 130 or transfers a ring frame 180 from the forwarding circuit 121 to the multiplexing circuit 131. In the wrap mode, it transfers a ring frame 180 from the forwarding circuit 120 to the multiplexing circuit 131 or transfers a ring frame 180 from the forwarding circuit 121 to the multiplexing circuit 130. The mode of the protection switch 150 is changed by the ring protection processing circuit 140.
The ring protection processing circuit 140 monitors the condition of junction links to adjacent nodes. If a fault occurs in the junction links, the ring protection processing circuit 140 changes the mode of the protection switch 150 from the pass-through mode to the wrap mode and transfers a ring frame 180 containing information on the faulty condition to the multiplexing circuits 130 and 131. At this time, frame at tribute 185 of the ring frame 180 is “fault notice frame”, the address of this node is assigned as transmission source ring node address 181, and the corresponding adjacent ring node address is stored as transmission destination ring node address 181.
If the ring protection processing circuit 140 receives through the forwarding circuit 120 or 121 a ring frame 180 containing information on a fault from one adjacent ring node 100, it transfers the ring frame 180 containing the information to the multiplexing circuit 130 or 131 in order to transfer the ring frame 180 to the other adjacent ring node 100 in the same ring from which the ring frame 180 has been received. At this time, the address of this node is stored as transmission source ring node address 181 in the ring frame 180.
Each of the multiplexing circuits 130 and 131 multiplexes ring frames 180 from the packet switch 160, the protection switch 150 and the ring protection processing circuit 140 and transfers the multiplexed ring frames to the inner ring 101-in or outer ring 102-out.
FIGS. 16 and 17 show a two-fiber-ring network formed of eight ring nodes 100. It is assumed here that the inner ring 101 transfers ring frames 180 clockwise and the outer ring 102 transfers ring frames 180 counterclockwise.
A case of transfer of a unicast user frame from a terminal 210 to a terminal 211 in the ring network will be described with reference to FIG. 16.
When a ring node 100-7 receives a user frame from terminal 210, it forms a ring frame 180 by setting “ring node 100-4” as transmission destination ring node address 181, “ring node 100-7” as transmission source ring node address 182, “outer ring” as ring ID 183, and designated values as TTL 184, frame attribute 185 and flow ID 186, and transfers this ring frame 180 through the outer ring 102. The ring frame 180 transferred to the outer ring 102 is transferred to the ring node 100-4 via a route 201 including ring nodes 100-6 and 100-5. In each of the ring nodes 100-6 and 100-5, 1 is subtracted from the TTL in the ring frame 180. The ring node 100-4 converts the transferred ring frame 180 into a user frame and transfers this user frame to the terminal 211.
A case of transfer of a multicast/broadcast user frame from the terminal 210 to the terminal 211 will be described with reference to FIG. 17.
When the ring node 100-7 receives a user frame from terminal 210, it forms a ring frame 180 by setting “multicast/broadcast address” as transmission destination ring node address 181, “ring node 100-7” as transmission source ring node address 182, “outer ring” as ring ID 183, and designated values as TTL 184, frame attribute 185 and flow ID 186, and transfers this ring frame 180 to the outer ring 102. The ring frame 180 transferred to the outer ring 102 is transferred to the ring node 100-7 via a route 202 including the ring nodes 100-6, 100-5, 100-4, 100-3, 100-2, 100-1, and 100-8. In each of the ring nodes 100-6, 100-5, 100-4, 1003, 100-2, 100-1, and 100-8, copies of the ring frame 180 are made: one copy being converted into a user frame and transmitted to a suitable terminal; and another copy being transferred to the adjacent ring node while 1 is subtracted from the TTL 184. The ring node 100-7 discards the ring frame 180 since the transmission source ring node address 181 in the ring frame 180 and the transmission ring ID 183 coincide with the address of this node and the outer ring through which the ring frame 180 has been received.
FIGS. 18 and 19 show protection in a case where a fault occurs in the inner ring 101 or the outer ring 102 between the ring nodes 100-5 and 100-6 when a ring frame 180 is transferred from the ring node 100-7 to the ring node 100-4 via a route 301 by using the inner ring 101. The configuration of the network shown in FIGS. 18 and 19 is the same as that shown in FIGS. 16 and 17.
The ring protection processing circuit 140 in each of the ring nodes 100-5 and 100-6 detects the fault and sets the protection switch 150 of the node in the wrap mode to transfer the ring frame 180 as described below. The ring frame 180 to be transferred from the ring node 100-7 to the ring node 100-4 is transferred to the ring node 100-6 through the outer ring 102 and sent back from the ring node 100-6 by being transferred through the inner ring 101. The returned ring frame 180 is transferred to the ring node 100-5 via the ring nodes 100-7, 100-8, and 100-1 to 100-4. The ring frame 180 is again sent back from the ring node 100-5 by means of the outer ring 102 to be transferred to the ring node 100-4 via a route 302.
Thus, the conventional ring network using SRP has a loop configuration but can avoid looping of a ring frame input to the network by discarding the ring frame when the ring frame reaches the transmission source ring node or when the TTL value becomes zero. Also, in the case of occurrence of a fault in the ring, the faulty-end ring nodes reverse the ring frame transfer direction to ensure high-speed protection.
In a case where multiple rings are connected as an expansion of the single two-fiber ring, when a broadcast/multicast frame flows into the two-fiber ring operating as a relay ring, it cannot be discarded unless the TTL counter becomes zero, since no ring node having the transmission source ring node address exists in the ring, as long as discarding is based on the conventional principle. There is a possibility of the ring frame making one round or more of the relay ring, depending on the initial setting of the TTL counter, that is, the same ring frame may be transmitted two or more times to the ring node which is to receive the ring frame, resulting in a reduction in network efficiency.
If, in a similar network, a fault occurs at one of inter-ring bridge nodes connected between a plurality of rings when a ring frame is being transferred to the transmission destination ring node via some of the plurality of rings and the inter-ring bridge node, protection cannot be effected in the system even if a usable physical path exits. This is because another of the inter-ring bridge nodes capable of providing a bypass route cannot recognize the ring frame for which bridging has been performed by the faulty inter-ring bridge node.